Ultrathin atomic layer deposition film accuracy thickness control

ABSTRACT

Methods for depositing ultrathin films by atomic layer deposition with reduced wafer-to-wafer variation are provided. Methods involve exposing the substrate to soak gases including one or more gases used during a plasma exposure operation of an atomic layer deposition cycle prior to the first atomic layer deposition cycle to heat the substrate to the deposition temperature.

BACKGROUND

Various thin film layers for semiconductor devices may be deposited withatomic layer deposition (ALD) processes. However, existing ALD processesmay not be suitable for depositing ultrathin films having a thicknessless than about 50 Å. For example, many existing ALD processes fordepositing ultrathin films result in a high wafer-to-wafer variationbetween films deposited from substrate to substrate.

SUMMARY

Methods and apparatuses for processing semiconductor substrates areprovided herein. One aspect involves a method for depositing a siliconoxide film by atomic layer deposition on a semiconductor substrate by:(a) inserting a substrate into a chamber; (b) after inserting thesubstrate into the chamber and prior to performing a first cycle ofatomic layer deposition at a deposition temperature, raising thesubstrate's temperature to about the deposition temperature by exposingthe substrate to a soak gas for a duration of about 500 seconds or less;and (c) performing the atomic layer deposition, whereby a cycle of theatomic layer deposition includes exposing the substrate to asilicon-containing precursor in a non-plasma environment for a durationsufficient to substantially adsorb the silicon-containing precursor tothe surface of the substrate and exposing the substrate to an oxidant ina plasma environment to form at least a portion of the silicon oxidefilm; where soaking the substrate includes exposing the substrate to asoak gas including only one or more gases used when exposing thesubstrate to the oxidant in the plasma environment during the atomiclayer deposition cycle to form the at least a portion of the siliconoxide film; and where the thickness of the silicon oxide film depositedby the atomic layer deposition is less than about 5 nm.

The soak gas in (b) may contain only a gas or gases used when exposingthe substrate to the oxidant in the plasma environment to form the atleast a portion of the silicon oxide film. In some embodiments, the soakgas in (b) includes two or more gases, and no other gases, used whenexposing the substrate to the oxidant in the plasma environment to formthe at least a portion of the silicon oxide film, and where the two ormore gases are present in the soak gas in substantially the sameproportion as they are in the oxidant.

In various embodiments, the soak gas in (b) is selected from the groupconsisting of argon, nitrogen, oxygen, nitrous oxide, and combinationsthereof. The soak gas in (b) may include no helium.

The flow rate of the soak gas in (b) may be within about 10% of amaximum flow rate achievable by the chamber. In some embodiments, theflow rate of the soak gas in (b) is at least about 15 slm. In variousembodiments, the flow rate of the soak gas in (b) is at least about 25%to about 200% of the flow rate of the one or more gases used whenexposing the substrate to the oxidant in the plasma environment duringthe atomic layer deposition cycle.

Wafer-to-wafer variation of the average silicon oxide film thicknessover the surface of the substrate may be less than about ±2 Å.

In various embodiments, (c) includes performing two or more atomic layerdeposition cycles to deposit the silicon oxide film on the substrate. Insome embodiments, between two and about fifty atomic layer depositioncycles are performed.

The silicon-containing precursor may be selected from the groupconsisting of silane, disilane, trisilane, tetrasilane,halogen-substituted versions of any of the foregoing silanes,amine-substituted versions of any of the foregoing silanes, andtrisilylamine. The oxidant may be selected from the group consisting ofoxygen, nitrous oxide, and combinations thereof. The atomic layerdeposition may be performed at a temperature of between about 30° C. andabout 70° C. In various embodiments, the cycle of the atomic layerdeposition further includes purging the chamber between each exposingoperation.

Another aspect involves a method for depositing a film by atomic layerdeposition on a semiconductor substrate by: (a) inserting a substrateinto a chamber; and (b) after inserting the substrate into the chamberand prior to performing a first cycle of atomic layer deposition at adeposition temperature, raising the substrate's temperature to about thedeposition temperature by exposing the substrate to a soak gas for aduration of about 500 seconds or less; and (c) performing the atomiclayer deposition, where a cycle of the atomic layer deposition includesexposing the substrate to a precursor in a non-plasma environment for aduration sufficient to substantially adsorb the precursor to the surfaceof the substrate, and exposing the substrate to a second reactant in aplasma environment to form at least a portion of the film; and wheresoaking the substrate includes exposing the substrate to a soak gasincluding only one or more gases used when exposing the substrate to thesecond reactant in the plasma environment during the atomic layerdeposition cycle to form the at least a portion of the film; and wherethe thickness of the film deposited by the atomic layer deposition isless than about 5 nm.

The soak gas in (b) may contain only a gas or gases used when exposingthe substrate to the second reactant in the plasma environment to formthe at least a portion of the film. In various embodiments, the soak gasin (b) includes two or more gases, and no other gases, used whenexposing the substrate to the second reactant in the plasma environmentto form the at least a portion of the film, and where the two or moregases are present in the soak gas in substantially the same proportionas they are in the second reactant.

The soak gas in (b) may be selected from the group consisting of argon,nitrogen, oxygen, nitrous oxide, and combinations thereof. The soak gasin (b) may include no helium.

In various embodiments, the flow rate of the soak gas in (b) is within10% of a maximum flow rate achievable by the chamber. In someembodiments, the flow rate of the soak gas in (b) is at least about 15slm. In various embodiments, the flow rate of the soak gas in (b) is atleast about 25% to about 200% of the flow rate of the one or more gasesused when exposing the substrate to the oxidant in the plasmaenvironment during the atomic layer deposition cycle.

Wafer-to-wafer variation of the average film thickness over the surfaceof the substrate may be less than about ±2 Å. In some embodiments (c)includes performing two or more atomic layer deposition cycles todeposit the film on the substrate. For example, in some embodiments,between two and about fifty atomic layer deposition cycles areperformed.

The film deposited by the atomic layer deposition may be selected fromthe group consisting of silicon oxide, silicon nitride, silicon carbide,metal oxide, doped silicon oxide, doped silicon nitride, doped siliconcarbide, and doped metal oxide. In some embodiments, the film depositedby the atomic layer deposition is an oxide and the atomic layerdeposition is performed at a temperature of about 50° C. In someembodiments, the film deposited by the atomic layer deposition is anitride or carbide and the atomic layer deposition is performed at atemperature of between about 200° C. and about 300° C.

The precursor may include a chemical selected from the group consistingof silicon, metals, electron-donating atoms, and electron-donatinggroups. In various embodiments, the second reactant is a reductant oroxidant.

The cycle of the atomic layer deposition may further include purging thechamber between each exposing operation.

Another aspect involves an apparatus for processing semiconductorsubstrates, the apparatus including: (a) one or more stations, eachreaction station including a pedestal for holding a substrate; (b) atleast one outlet for coupling to a vacuum; (c) one or more process gasinlets for coupling to precursor and reactant sources; (d) a robot forinserting substrates into the one or more reaction chambers; and (e) acontroller for controlling operations in the apparatus, includingmachine-readable instructions for: (i) inserting a substrate into one ofthe one or more stations, (ii) introducing a soak gas for a duration ofabout 500 seconds or less; (iii) introducing a silicon-containingprecursor for a duration sufficient to substantially adsorb thesilicon-containing precursor onto the surface of the substrate; (iv)introducing a second reactant into the one or more reaction chambers andigniting a plasma; and (v) repeating (iii) and (iv) to form a film onthe substrate, the film having a thickness less than about 5 nm, wherethe soak gas in (ii) includes only one or more gases used in (iv).

The controller may further include machine-readable instructions forperforming (ii) at least once after each new substrate is inserted intoone of the one or more stations by the robot. In some embodiments, theapparatus includes two or more stations.

These and other aspects are described further below with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram depicting operations of a method inaccordance with disclosed embodiments.

FIG. 2 is a timing sequence diagram showing an example of cycles in amethod in accordance with disclosed embodiments.

FIG. 3 is a schematic diagram of an example process station forperforming disclosed embodiments.

FIG. 4 is a schematic diagram of an example process tool for performingdisclosed embodiments.

FIG. 5 is graph depicting experimental results from an experimentconducted in accordance with disclosed embodiments.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the presented embodiments. Thedisclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Manufacture of semiconductor devices typically involves depositing oneor more conformal thin films on a substrate in an integrated fabricationprocess. For example, some front-end-of-the-line processes may involvedeposition of conformal films by atomic layer deposition (ALD). ALD is atechnique that deposits thin layers of material using sequentialself-limiting reactions. ALD processes use surface-mediated depositionreactions to deposit films on a layer-by-layer basis in cycles. As anexample, an ALD cycle may include the following operations: (i)delivery/adsorption of a silicon-containing precursor, (ii) purging ofsilicon-containing precursor from the chamber, (iii) delivery of asecond reactant and ignite plasma, and (iv) purging of byproducts fromthe chamber.

As devices shrink, conformal layers become thinner and fewer and fewerALD cycles are used to deposit a film on a substrate. As a result, it isdesirable to accurately control film thickness from substrate tosubstrate. Film thickness of a substrate may be measured by taking anaverage film thickness over the surface of the substrate. Variation inthickness from substrate to substrate may be known as “wafer-to-wafervariation.” In thicker films deposited by ALD, variations in thicknessin initial cycles of ALD has a smaller impact than in thinner filmsbecause there are more cycles of ALD performed in depositing a thickerfilm. For example, a wafer-to-wafer variation of ±5 Å in thicknessbetween films deposited to a thickness of 500 Å is a small fractioncompared to a wafer-to-wafer variation of ±5 Å in thickness betweenfilms having a thickness of 10 Å. Thus, for deposition of ultrathinfilms, such as films having an average film thickness less than about 50Å, accurate control of wafer-to-wafer variation is of particularinterest. Ultrathin films may be used in various applications, such asfabrication of front-end-of-line spacers, plug liners, and cap layers.As devices shrink, other forms of variation also become problematic.Such variations include within wafer variation: i.e., layer thicknessvariations from one position to another position on a single wafer.While most of the discussion herein concerns wafer-to-wafer variations,the disclosed improvements may be equally applicable to other forms ofvariation.

Variation may depend on a number of factors, including the chamberconditions prior to performing ALD cycles on a substrate. ConventionalALD methods typically begin by placing a substrate on a pedestal in achamber or station, which may be part of an apparatus, reactor, or toolfor fabricating semiconductor substrates. To perform ALD at a desireddeposition temperature, the pedestal is set to a desired depositiontemperature and once the substrate is placed on the pedestal, thesubstrate is heated such that the substrate temperature is approximatelythe same as the pedestal temperature. Prior to being placed on thepedestal, the substrate may be at a temperature different from that ofthe pedestal temperature. For example, substrate temperatures may be atroom temperature, such that the substrate temperature is raised to adeposition temperature on the pedestal. Conventional methods forstabilizing the substrate temperature involved exposing the substrate tocertain conditions to more efficiently bring the substrate temperatureup to a temperature at or near the deposition temperature. Exposure tothese conditions is sometimes called “soak.” To increase throughput andreduce the time required for the substrate temperature to be raised,conventionally the wafer is exposed to helium, which has a high thermalconductivity, to stabilize the substrate temperature. However,conventional methods contaminate or increase the wafer-to-wafervariation of films deposited between substrates. For example, althoughthe chamber may be purged after the substrate is exposed to helium, somehelium may still be present in the chamber such that when the plasmaignites, the plasma has a slight purple color, which is consistent withhelium plasma, and nucleation and incubation periods for the ALD processare affected, thereby increasing wafer-to-wafer variation betweensubstrates.

Provided herein are methods of soaking a substrate prior to performingALD to reduce wafer-to-wafer variation between substrates. Methods maybe used to deposit ultrathin films, which are defined as films having athickness of about 50 Å or less, or about 30 Å or less, or about 20 Å orless, or about 10 Å or less. Methods involve exposing the substrate to asoak gas including one or more gases used with the second reactant of anALD cycle. In various embodiments, the soak gas only includes gases usedwith the second reactant of an ALD cycle. Deposited films are uniformfrom substrate to substrate, with wafer-to-wafer variation less thanabout ±2Å for deposition of ultrathin films, or less than about ±1 Å. Invarious embodiments, wafer-to-wafer variation of less than about ±2 Å isachieved where between about 2 and about 10 cycles of ALD are performed.Disclosed embodiments are suitable for deposition of any film depositedby ALD, such as dielectric films, metal films, semiconductor films, andfilms of any material used in the fabrication of semiconductorsubstrates. For example, disclosed embodiments may be used to depositsilicon oxide (SiO), silicon nitride (SiN), silicon carbide (SiC),silicon oxynitride (SiON), silicon oxycarbonitride (SiOCN), metal oxide,doped silicon oxide, doped silicon nitride, doped silicon carbide, ordoped metal oxide. In some embodiments, disclosed embodiments may beused to deposit titanium nitride, tantalum nitride, tungsten, aluminumoxide, and aluminum nitride. The deposited materials may have normalstoichiometry (e.g., SiO₂) or variants thereof.

The methods provided herein involve deposition by ALD. Unlike a chemicalvapor deposition (CVD) technique, ALD processes use surface-mediateddeposition reactions to deposit films on a layer-by-layer basis. In oneexample of an ALD process, a substrate surface, including a populationof surface active sites, is exposed to a gas phase distribution of afirst precursor in a dose provided to a process station housing thesubstrate. Molecules of this first precursor are adsorbed onto thesubstrate surface, including chemisorbed species and/or physisorbedmolecules of the first precursor. It should be understood that when thecompound is adsorbed onto the substrate surface as described herein, theadsorbed layer may include the compound as well as derivatives of thecompound. For example, an adsorbed layer of a silicon-containingprecursor may include the silicon-containing precursor as well asderivatives of the silicon-containing precursor. In certain embodiments,an ALD precursor dose partially saturates the substrate surface. In someembodiments, the dose phase of an ALD cycle concludes before precursorcontacts the substrate to evenly saturate the surface. Typically, theprecursor flow is turned off or diverted at this point, and only purgegas flows. By operating in this sub-saturation regime, the ALD processreduces the cycle time and increases throughput. However, becauseprecursor adsorption is not saturation limited, the adsorbed precursorconcentration may vary slightly across the substrate surface. Examplesof ALD processes operating in the sub-saturation regime are provided inU.S. patent application Ser. No. 14/061,587, filed Oct. 23, 2013, titled“SUB-SATURATED ATOMIC LAYER DEPOSITION AND CONFORMAL FILM DEPOSITION,”which is incorporated herein by reference in its entirety. After a firstprecursor dose, the reactor is then evacuated to remove any firstprecursor remaining in gas phase so that only the adsorbed speciesremain. A second reactant is introduced to the reactor so that some ofthese molecules react with the first precursor adsorbed on the surface.In some processes, the second reactant reacts immediately with theadsorbed first precursor. In other embodiments, the second reactantreacts only after a source of activation is applied, such as plasma. Invarious embodiments described herein, the second reactant reacts withthe adsorbed first precursor when a plasma is ignited. The reactor maythen be evacuated again to remove unbound second reactant molecules. Insome implementations, the ALD methods include plasma activation. Asdescribed herein, the ALD method and apparatuses described herein may beconformal film deposition (CFD) methods, which are described generallyin U.S. patent application Ser. No. 13/084,399 (now U.S. Pat. No.8,728,956), filed Apr. 11, 2011, and titled “PLASMA ACTIVATED CONFORMALFILM DEPOSITION,” and in U.S. patent application Ser. No. 13/084,305,filed Apr. 11, 2011, and titled “SILICON NITRIDE FILMS AND METHODS,”which are herein incorporated by reference in its entireties.

The concept of an ALD “cycle” is relevant to the discussion of variousembodiments herein. Generally a cycle is the minimum set of operationsused to perform a surface deposition reaction one time. The result ofone cycle is production of at least a partial silicon oxide film layeron a substrate surface. Typically, an ALD cycle includes operations todeliver and adsorb at least one reactant to the substrate surface, andthen react the adsorbed reactant with one or more reactants to form thepartial layer of film. The cycle may include certain ancillaryoperations such as sweeping one of the reactants or byproducts and/ortreating the partial film as deposited. Generally, a cycle contains oneinstance of a unique sequence of operations. ALD cycles may be used tobuild film thickness.

FIG. 1 provides a process flow diagram for performing operations inaccordance with disclosed embodiments. FIG. 2 is a timing sequencediagram of example pulses in accordance with disclosed embodiments. FIG.2 shows phases in an example ALD process 200, for various processparameters, such as carrier gas flow, first precursor flow, plasma, andsecond reactant flow. FIG. 2 includes two deposition cycles 210A and210B and a pre-ALD soak 250 prior to the first ALD cycle (depositioncycle 210). The lines indicate when the flow or plasma is turned on andoff, accordingly. FIGS. 1 and 2 will be described together below.

In operation 101 of FIG. 1, a substrate is provided to a processchamber. The process chamber includes a pedestal or substrate holderwhere the substrate is placed. The substrate may be a silicon wafer,e.g., a 200-mm wafer, a 300-mm wafer, or a 450-mm wafer, includingwafers having one or more layers of material, such as dielectric,conducting, or semi-conducting material deposited thereon. Substratesmay have “features” such as via or contact holes, which may becharacterized by one or more of narrow and/or re-entrant openings,constrictions within the feature, and high aspect ratios. The featuremay be formed in one or more of the above described layers. One exampleof a feature is a hole or via in a semiconductor substrate or a layer onthe substrate. Another example is a trench in a substrate or layer. Invarious embodiments, the feature may have an under-layer, such as abarrier layer or adhesion layer. Non-limiting examples of under-layersinclude dielectric layers and conducting layers, e.g., silicon oxides,silicon nitrides, silicon carbides, metal oxides, metal nitrides, metalcarbides, and metal layers.

In some embodiments, the feature may have an aspect ratio of at leastabout 2:1, at least about 4:1, at least about 6:1, at least about 10:1,or higher. The feature may also have a dimension near the opening, e.g.,an opening diameter or line width of between about 10 nm to 500 nm, forexample between about 25 nm and about 300 nm. Disclosed methods may beperformed on substrates with features having an opening less than about150 nm. A feature via or trench may be referred to as an unfilledfeature or a feature. A feature that may have a re-entrant profile thatnarrows from the bottom, closed end, or interior of the feature to thefeature opening.

During operation 101, the pedestal is set to a deposition temperature.For example, the pedestal may be set to the temperature to be usedduring deposition of a film by ALD in subsequent operations. In variousembodiments, the pedestal is set to a temperature greater than roomtemperature, or greater than about 20° C., or greater than about 25° C.The deposition temperature depends on the type of film to be depositedon the substrate and the chemistry used for depositing the film. Forexample, in some embodiments, deposition temperature for depositing anoxide may be less than about 100° C., or less than about 50° C., orabout 50° C. In some embodiments, deposition temperature for depositinga nitride or carbide may be less than about 400° C., or less than about300° C., or less than about 200° C., or between about 200° C. and about300° C. In some embodiments, deposition temperature may be greater thanabout 400° C.

In operation 150, the substrate is exposed to a soak gas prior toperforming the first cycle of ALD on the substrate. The substrate isexposed to the soak gas to raise the temperature of the substrate to atemperature at or near the deposition temperature. For example, asubstrate inserted into to the process chamber from an outsideenvironment may be at a room temperature of about 20° C., and thesubstrate is exposed to a soak gas to raise the temperature of thesubstrate to a temperature of about 50° C. for oxide deposition. Theprocess of raising the substrate temperature when exposed to the soakgas is referred to as “soak.”

In various embodiments, the soak gas is helium-free, such that no heliumis present in the process chamber during operation 150. The soak gas maybe a carrier gas or any second reactant used in ALD, or any combinationthereof. In various embodiments, the soak gas is one or more gases usedwith the second reactant in the plasma step of the ALD cycle, which isdescribed below with respect to operation 111. Additional examples ofsoak gases include argon (Ar), helium (He), hydrogen (H₂), xenon (Xe),krypton (Kr), nitrogen (N₂), oxygen (O₂), nitrous oxide (N₂O), ammonia(NH₃), hydrazine, ozone (O₃), nitric oxide (NO), nitrogen dioxide (NO₂),carbon monoxide (CO), carbon dioxide (CO₂), sulfur monoxide (SO), andwater (H₂O). In some implementations, the soak gas contains no gasesother than gases present when the second reactant is introduced duringthe ALD cycle. For example, if the only gases present during this phaseare argon, oxygen, and nitrous oxide, the soak gas would include one ormore of argon, oxygen, and nitrous oxide, but no other gases.

For deposition of silicon oxide, the soak gas may be an oxidant and/or acarrier gas used when the substrate is exposed to the oxidant in aplasma environment in an ALD cycle. Examples of soak gases fordeposition of silicon oxide include, but are not limited to, Ar, N₂, O₂,N₂O, O₃, peroxides including hydrogen peroxide (H₂O₂), H₂O, alcoholssuch as methanol, ethanol and isopropanol, NO, NO₂, CO, and CO₂. In someembodiments, the oxidizer may be a mixture of O₂ and a weak oxidizersuch as N₂O, CO, CO₂, NO, NO₂, SO, SO₂, C_(x)H_(y)O_(z) and/or H₂O.

For deposition of silicon nitride, the soak gas may be anitrogen-containing reactant and/or a carrier gas used when thesubstrate is exposed to the nitrogen-containing reactant in a plasmaenvironment in an ALD cycle. Example soak gases for deposition ofsilicon nitride include Ar, H₂, N₂, and NH₃. Additional examples ofnitrogen-containing reactants include compounds containing at least onenitrogen, for example, hydrazine, amines (amines bearing carbon) such asmethylamine, dimethylamine, ethylamine, isopropylamine, t-butylamine,di-t-butylamine, cyclopropylamine, sec-butylamine, cyclobutylamine,isoamylamine, 2-methylbutan-2-amine, trimethylamine, diisopropylamine,diethylisopropylamine, di-t-butylhydrazine, as well as aromaticcontaining amines such as anilines, pyridines, and benzylamines. Aminesmay be primary, secondary, tertiary or quaternary (for example,tetraalkylammonium compounds). A nitrogen-containing reactant cancontain heteroatoms other than nitrogen, for example, hydroxylamine,t-butyloxycarbonyl amine and N-t-butyl hydroxylamine arenitrogen-containing reactants.

The composition of soak gases used may depend on the composition usedwhen the substrate is exposed to the second reactant in a plasmaenvironment of an ALD cycle. In some embodiments, the soak gas containsonly carrier gas. In some embodiments, the soak gas contains only thesecond reactant.

All percentages and ratios listed herein are by flow rate. In someembodiments, the composition of soak gases in operation 150 is identicalto the composition of gases in operation 111. In some embodiments, thecomposition of soak gases in operation 150 is different from thecomposition of gases in operation 111. For example, the flow rate ofsoak gases in operation 150 may be at least about 25% to at least about200% of the flow rate of the gases in operation 111. In someembodiments, the composition of soak gases in operation 150 includes acarrier gas and the second reactant, where the second reactant mayinclude one or more gases, and the flow rate of the carrier gas may bebetween about 25% and about 200% of the flow rate of the carrier gas inoperation 111 Likewise, the flow rate of the second reactant inoperation 150 may be at least about 25% to about 200% of the flow rateof the second reactant in operation 111.

For example, in deposition of oxides, the composition of soak gases mayinclude argon, nitrogen, and oxygen. The flow rate of each of argon,nitrogen, and oxygen may be at least about 25% to about 200% of the flowrate of argon, nitrogen, and oxygen respectively used in operation 111.In another example, the composition of soak gases used prior todepositing an oxide may include nitrous oxide and oxygen such that theflow rate ratio of nitrous oxide to oxygen may be between about 1:5 andabout 2:1.

In deposition of nitrides, example compositions of soak gases mayinclude compositions having a carrier gas and a nitrogen-containing gas.In deposition of metal compounds, example compositions of soak gases mayinclude compositions including a carrier gas and a nitrogen-containinggas. The carrier gas and the nitrogen-containing gas may be at leastabout 25% to about 200% of the flow rate of the respective gas used whenthe carrier gas and nitrogen-containing gas are used in operation 111.

In deposition of carbides, example compositions of soak gases mayinclude a carrier gas, and a carbon-containing gas. The carrier gas andthe carbon-containing gas may be at least about 25% to about 200% of theflow rate of the respective gas used when the carrier gas andcarbon-containing gas are used in operation 111.

The flow rate of the soak gases during operation 150 may be at leastabout 500 sccm for a chamber including four stations, each station ofwhich includes a substrate. In some embodiments, the flow rate of thesoak gases during operation 150 is within about 10% of a maximum flowrate achievable by the chamber. For example, the flow rate of the soakgases may be at least about 15 slm, or at least about 20 slm, or betweenabout 15 slm and about 20 slm, for example about 17 slm.

In operation 150, the substrate is exposed to the soak gas or gases fora short period of time. A short period is defined as a duration lessthan about 150 seconds, or less than about 100 seconds, or less thanabout 60 seconds. For example, the substrate may be exposed to the soakgas or gases for a duration between about 5 seconds and about 60seconds, for example, about 5 seconds.

Operation 150 may be performed each time a new substrate is insertedinto a process chamber in the apparatus, which may be a multi-stationtool including one or more stations. In some embodiments, the apparatusincludes four stations for processing substrates. Further description ofexample apparatuses are described below with respect to FIGS. 3 and 4.In various embodiments, every time a new substrate is inserted into thetool, such as into one of stations in a multi-station tool, operation150 may be performed. Operation 150 thus may be performed before everyfirst cycle of ALD for any single substrate in a chamber of amulti-station tool. Operation 150 may be performed even if othersubstrates in a multi-station tool have partially deposited ALD films.In some embodiments, the chamber is purged after operation 150. Itshould be understood that multi-station tools may be operated in variousmodes. In some modes, all substrates are inserted and then processed tocompletion before any substrate is removed. In other modes, onesubstrate is removed and another is inserted each time the substratesindex from one station to the next within the tool. In other modes, twosubstrates are added and two are removed, but at least two others remainduring certain index operations. Other modes can be employed.

FIG. 2 shows a pre-ALD soak 250 prior to the first ALD deposition cycle210. During pre-ALD soak 250, which may correspond to operation 150 ofFIG. 1, the first precursor is turned off, and the plasma is turned off,while the purge gas or carrier gas and second reactant are turned on.Note that the on/off condition for the pre-ALD soak 250 is the same asthe on/off conditions shown for the second reactant with plasma exposurephases 260A and 260B. Note that in some embodiments, the carrier gas isnot flowed during the pre-ALD soak 250. As explained elsewhere, variouscombinations of the gases employed in operation 260B may be used in thesoak.

Returning to FIG. 1, operations 103-113 may be operations of an ALDcycle. During operations 103-113, an inert gas may be flowed. In someembodiments, the inert gas is flowed during operations 150-113.Disclosed embodiments may be performed at a chamber pressure betweenabout 0.1 Torr and about 20 Torr. In various embodiments, the inert gasis used as a carrier gas. Example carrier gases include argon (Ar),helium (He), hydrogen (H₂), oxygen (O₂), krypton (Kr), xenon (Xe), andneon (Ne). The inert gas may be provided to assist with pressure and/ortemperature control of the process chamber, evaporation of a liquidreactant, more rapid delivery of the reactant and/or as a purge gas forremoving process gases from the process chamber and/or process chamberplumbing. The example sequences in FIG. 2 shows a carrier gas, which iscontinuously flowed during the entire process.

In operation 103 of FIG. 1, the substrate is exposed to a firstprecursor such that the first precursor adsorbs on to the substratesurface. In some embodiments, the first precursor adsorbs onto thesubstrate surface in a self-limiting manner such that once active sitesare occupied by the first precursor, little or no additional firstprecursor will be adsorbed on the substrate surface. In variousembodiments, when the first precursor is flowed to the station, thefirst precursor adsorbs onto active sites on the surface of thesubstrate, forming a thin layer of the first precursor on the surface.In various embodiments, this layer may be less than a monolayer, and mayhave a thickness between about 0.2 Å and about 0.8 Å.

In various embodiments, the first precursor includes anelectron-donating atom or electron-donating group. In variousembodiments, the first precursor is a silicon-containing precursor or ametal-containing precursor. In some embodiments, the first precursor isa silicon-containing precursor suitable for depositing a silicon oxidefilm by ALD. The first precursor may also be a mixture of two or morecompounds. In some embodiments, the silicon-containing precursor ischosen depending on the type of silicon-containing film to be deposited.

Example silicon-containing precursors include, but are not limited to,silanes, polysilanes, halosilanes, and aminosilanes. A silane containshydrogen and/or carbon groups, but does not contain a halogen. Apolysilane may have the formula (H₃Si—(SiH₂)_(n)—SiH₃), where n≥1.Examples of silanes include silane (SiH₄), disilane (Si₂H₆), trisilane,tetrasilane and organo silanes such as methylsilane, ethylsilane,isopropylsilane, t-butylsilane, dimethylsilane, diethylsilane,di-t-butylsilane, allylsilane, sec-butylsilane, thexylsilane,isoamylsilane, t-butyldisilane, di-t-butyldisilane, tetra-ethyl-ortho-silicate (also known as tetra-ethoxy-silane or TEOS) and the like.

A halosilane contains at least one halogen group and may or may notcontain hydrogens and/or carbon groups. A halosilane may have a formulaSiX_(a)H_(y) whereby X═Cl, F, I, or Br, and a+y=4, where a≥1. Ahalosilane may have a formula SiX_(a)H_(y)(CH₃)_(z) where X═Cl, F, I, orBr, and a+y+z=4, where a≥1. Examples of halosilanes are iodosilanes,bromosilanes, chlorosilanes and fluorosilanes. Although halosilanes,particularly fluorosilanes, may form reactive halide species that canetch silicon materials, in certain embodiments described herein, thesilicon-containing precursor is not present when a plasma is struck.Specific chlorosilanes are tetrachlorosilane (SiCl₄), trichlorosilane(HSiCl₃), dichlorosilane (H₂SiCl₂), monochlorosilane (ClSiH₃),chloroallylsilane, chloromethylsilane, dichloromethylsilane,chlorodimethylsilane, chloroethylsilane, t-butylchlorosilane,di-t-butylchlorosilane, chloroisopropylsilane, chloro- sec-butylsilane,t-butyldimethylchlorosilane, thexyldimethylchlorosilane,monochlorotrimethylsilane, and the like.

An aminosilane includes at least one nitrogen atom bonded to a siliconatom, but may also contain hydrogens, oxygens, halogens and carbons.Examples of aminosilanes are mono-, di-, tri- and tetra-aminosilane(H₃Si(NH₂)₄, H₂Si(NH₂)₂, HSi(NH₂)₃ and Si(NH₂)₄, respectively), as wellas substituted mono-, di-, tri- and tetra-aminosilanes, for example,t-butylaminosilane, methylaminosilane, tert-butylsilanamine, bis(tertiarybutylamino)silane (SiH₂(NHC(CH₃)₃)₂ (BTBAS), tert-butylsilylcarbamate, SiH(CH₃)—(N(CH₃)₂)₂, SiHCl—(N(CH₃)₂)₂, (Si(CH₃)₂NH)₃,di(sec-butylamino)silane (DSBAS), di(isopropylamido)silane (DIPAS),bis(diethylamino)silane (BDEAS), and the like. A further example of anaminosilane is trisilylamine (N(SiH₃)₃).

Examples of silicon-containing precursors for depositing silicon carbideinclude siloxanes, alkyl silane or hydrocarbon-substituted silane, or anitrogen-containing carbon-containing reactant. Example siloxanesinclude 2,4,6,8-tetramethylcyclotetrasiloxane (TMCTS),heptamethylcyclotetrasiloxane (HMCTS), silsesquioxane, disiloxanes, suchas pentamethyldisiloxane (PMDSO) and tetramethyldisiloxane (TMDSO), andtrisiloxanes such as hexamethyltrisiloxane, heptamethyltrisiloxane.Alkyl silanes include a central silicon atom with one or more alkylgroups bonded to it as well as one or more hydrogen atoms bonded to it.In some embodiments, any one or more of the alkyl groups contain 1-5carbon atoms. The hydrocarbon groups may be saturated or unsaturated(e.g., alkene (e.g., vinyl), alkyne, and aromatic groups). Examplesinclude but are not limited to trimethylsilane (3MS), triethylsilane,pentamethyl disilamethane ((CH₃)₂Si—CH₂—Si(CH₃)₃), and dimethylsilane(2MS). Additionally, disilanes, trisilanes, or other higher silanes maybe used in place of monosilanes. In some embodiments, one of the siliconatoms can have a carbon-containing or hydrocarbon group attached to it,and one of the silicon atoms can have a hydrogen atom attached to it.Example carbon-containing reactants including a nitrogen includemethyl-substituted disilazanes and trisilazanes, such astetramethyldisilazane and hexamethyl trisilazane.

Example first precursors used for depositing oxygen-doped siliconcarbide films include siloxanes such as cyclotetrasiloxanes such asheptamethylcyclotetrasiloxane (HMCTS) and tetramethylcyclotetrasiloxane.Other cyclic siloxanes can also include but are not limited tocyclotrisiloxanes and cyclopentasiloxanes. For depositing oxygen dopedsilicon carbide films, other examples of suitable precursors includelinear siloxanes such as, but not limited to, disiloxanes, such aspentamethyldisiloxane (PMDSO), tetramethyldisiloxane (TMDSO), hexamethyltrisiloxane, and heptamethyl trisiloxane. For undoped silicon carbide,examples of suitable precursors include monosilanes substituted with oneor more alkyl, alkene, and/or alkyne groups containing, e.g., 1-5 carbonatoms. Examples include but are not limited to trimethylsilane (3MS),dimethylsilane (2MS), triethylsilane (TES), andpentamethyldisilamethane. Additionally, disilanes, trisilanes, or otherhigher silanes may be used in place of monosilanes. An example of onesuch disilane from the alkyl silane class is hexamethyldisilane (HMDS).Another example of a disilane from the alkyl silane class can includepentamethyldisilane (PMDS). Other types of alkyl silanes can includealkylcarbosilanes, which can have a branched polymeric structure with acarbon bonded to a silicon atom as well as alkyl groups bonded to asilicon atom. Examples include dimethyl trimethylsilyl methane (DTMSM)and bis-dimethylsilyl ethane (BDMSE). For depositing nitrogen dopedsilicon carbide (SiNC) films, examples of suitable precursors include,e.g., alkyldisilazanes and possibly compounds including amino (—NH₂) andalkyl groups separately bonded to one or more silicon atoms.Alkyldisilazanes include silizanes and alkyl groups bonded to twosilicon atoms. An example includes 1,1,3,3-tetramethyldisilazane(TMDSN).

In some embodiments, the first precursor is a metal-containingprecursor. Example precursors may include metal alkylamines, metalalkoxides, metal alkylamides, metal halides, metal β-diketonates, metalcarbonyls, etc. The metal-containing precursors may also includeorganometallic compounds such as alkyl metal compounds as well as metalhalides having a high vapor pressure under deposition conditions. Suchcompounds exist in a vapor state and are readily delivered to thesubstrate and adsorb thereon. Some methods described herein may besuitable for ALD deposition of metal-containing films. Examples ofmetals include titanium (Ti), hafnium (Hf), zirconium (Zr), manganese(Mn), tungsten (W), and tantalum (Ta). Appropriate metal-containingprecursors will include the metal that is desired to be incorporatedinto the film. For example, a tantalum-containing layer may be depositedby reacting pentakis(dimethylamido)tantalum with ammonia or anotherreducing agent as a second reactant. Further examples ofmetal-containing precursors that may be employed includetrimethylaluminum, aluminum acetate, alkoxide, aluminum halidte,traethoxytitanium, tetrakis-dimethyl-amido titanium, hafniumtetrakis(ethylmethylamide), bis(cyclopentadienyl)manganese,bis(n-propylcyclopentadienyl)magnesium, tridimethylaminotitanium(TDMAT), tetraethoxytitanium, tetrakis-dimethyl-amido titanium, titaniumisopropoxide, titanium tetraisopropoxide, and compounds having theformula TiX_(n), where n is an integer between and including 2 through4, and X is a halide. Specific examples include TiI₄, TiCl₄, TiF₄, andTiBr₄.

Operation 103 may correspond to first precursor exposure phase 220A ofFIG. 2. During the first precursor exposure phase 220A, the firstprecursor is flowed with an optional purge or carrier gas, and theplasma and second reactant are turned off.

Returning to FIG. 1, in operation 105, the process chamber is optionallypurged to remove excess first precursor in gas phase that did not adsorbonto the surface of the substrate. Purging may involve a sweep gas,which may be a carrier gas used in other operations or a different gas.Sweeping the process station may avoid gas phase reactions where thesecond reactant is unstable to plasma activation or where unwantedspecies might be formed. Further, sweeping the process station mayremove surface adsorbed ligands that may otherwise remain andcontaminate the film. In some embodiments, purging may involveevacuating the chamber.

Operation 105 may correspond to purge phase 240A of FIG. 2. Purge phase240A may have any suitable duration. In some embodiments, increasing aflow rate of a one or more purge gases may decrease the duration ofpurge phase 240A. For example, a purge gas flow rate may be adjustedaccording to various reactant thermodynamic characteristics and/orgeometric characteristics of the process station and/or process stationplumbing for modifying the duration of purge phase 240A. In onenon-limiting example, the duration of a purge phase may be optimized byadjustment of the purge gas flow rate. This may reduce deposition cycletime, which may improve substrate throughput.

In some embodiments, purge phase 240A may include one or more evacuationsubphases for evacuating the process station. Alternatively, it will beappreciated that purge phase 240A may be omitted in some embodiments.Purge phase 240A may have any suitable duration, such as between about 0seconds and about 60 seconds, or about 0.01 seconds. In someembodiments, increasing a flow rate of a one or more purge gases maydecrease the duration of purge phase 240A. For example, a purge gas flowrate may be adjusted according to various reactant thermodynamiccharacteristics and/or geometric characteristics of the process stationand/or process station plumbing for modifying the duration of purgephase 240A. In one non-limiting example, the duration of a purge phasemay be adjusted by modulating sweep gas flow rate. This may reducedeposition cycle time, which may improve substrate throughput. After apurge, the silicon-containing precursors remain adsorbed onto thesubstrate surface.

Returning to FIG. 1, in operation 111, the substrate is exposed to asecond reactant and a plasma is ignited. The substrate is exposed to thesecond reactant for a duration sufficient to form a layer of material bya reaction on the surface of the substrate.

“Plasma” refers to a plasma ignited in a reaction chamber or remotelyand brought into the reaction chamber. Plasmas can include the reactantsdescribed herein and may include other agents, for example, a carriergas, or reactive species such as hydrogen gas. The reactants and otheragents may be present in a reaction chamber when a plasma is struck, ora remote plasma may be flowed into a chamber where the reactants arepresent and/or the reactants and/or carrier gas may be ignited into aplasma remotely and brought into the reaction chamber. A “plasma” ismeant to include any plasma known to be technologically feasible,including inductively-coupled plasmas and microwave surface waveplasmas.

In various embodiments, the plasma is an in-situ plasma, such that theplasma is formed directly above the substrate surface in the chamber.The in-situ plasma may be ignited at a power per substrate area betweenabout 0.2122 W/cm² and about 2.122 W/cm². For example, the power mayrange from about 600 W to about 6000 W for a chamber processing four 300mm wafers. Plasmas for ALD processes may be generated by applying aradio frequency (RF) field to a gas using two capacitively coupledplates. Ionization of the gas between plates by the RF field ignites theplasma, creating free electrons in the plasma discharge region. Theseelectrons are accelerated by the RF field and may collide with gas phasereactant molecules. Collision of these electrons with reactant moleculesmay form radical species that participate in the deposition process.Residual gases in the chamber that are not used to deposit the film byALD affect the ionization of gases during operation 111, therebyreducing the quality of the film being deposited. For example, if anyhelium is adsorbed on the surface of the substrate from priorprocessing, the plasma ignited in operation 111 has a purple colortypical of helium plasma and not usually used in ALD processes, therebycausing the deposited film on the film to be thinner than desired. Byusing a soak gas in operation 150 that is one or more gases used inoperation 111, the quality and thickness of the film to be deposited andformed in operation 111 is preserved. For example, for a deposition of asilicon oxide film, if the soak gas used in operation 150 is a mixtureof oxygen and nitrous oxide in a ratio of about 1:1, then if the samegases and same mixture ratios of gases are used in operation 111, thequality or thickness of the deposited silicon oxide film may not beaffected by the soak gas. This may insure that the soak gas may be usedmultiple times in the deposition process, such as every time a newsubstrate is inserted into a chamber, without affecting the depositedfilms.

During operation 111, it will be appreciated that the RF field may becoupled via any suitable electrodes. Non-limiting examples of electrodesinclude process gas distribution showerheads and substrate supportpedestals. It will be appreciated that plasmas for ALD processes may beformed by one or more suitable methods other than capacitive coupling ofan RF field to a gas. In some embodiments, the plasma is a remoteplasma, such that the second reactant is ignited in a remote plasmagenerator upstream of the station, then delivered to the station wherethe substrate is housed.

The second reactant may be an oxidant or reductant. In variousembodiments, the second reactant is an oxygen-containing reactant, or anitrogen-containing reactant, or a halogen-containing reactant, or acarbon-containing reactant, or a dopant. The second reactant may includeone or more of these compounds.

Example oxidants include, but are not limited to, ozone (O₃), peroxidesincluding hydrogen peroxide (H₂O₂), oxygen (O₂), water (H₂O), alcoholssuch as methanol, ethanol, and isopropanol, nitric oxide (NO), nitrousdioxide (NO₂) nitrous oxide (N₂O), carbon monoxide (CO) and carbondioxide (CO₂). Example oxygen-containing reactants include oxygen,ozone, nitrous oxide, nitric oxide, nitrogen dioxide, carbon monoxide,carbon dioxide, sulfur monoxide, sulfur dioxide, water,oxygen-containing hydrocarbons (C_(x)H_(y)O_(z)), etc.

A nitrogen-containing reactant contains at least one nitrogen, forexample, N₂, ammonia, hydrazine, amines (amines bearing carbon) such asmethylamine, dimethylamine, ethylamine, isopropylamine, t-butylamine,di-t-butylamine, cyclopropylamine, sec-butylamine, cyclobutylamine,isoamylamine, 2-methylbutan-2-amine, trimethylamine, diisopropylamine,diethylisopropylamine, ethylenediamine, tertbutylamine,di-t-butylhydrazine, as well as aromatic containing amines such asanilines, pyridines, and benzylamines. Amines may be primary, secondary,tertiary or quaternary (for example, tetraalkylammonium compounds). Anitrogen-containing reactant can contain heteroatoms other thannitrogen, for example, hydroxylamine, tertbutylamine (TBA),t-butyloxycarbonyl amine and N-t-butyl hydroxylamine arenitrogen-containing reactants.

In some embodiments, the flow rate of the second reactant may be betweenabout 0.1 slm and about 20 slm (e.g., between about 1 slm and about 10slm). In some embodiments, a carrier gas may be used during the exposureto the second reactant. An example of a suitable carrier gas is nitrogen(N₂), and if nitrogen is used as a carrier gas and co-flowed with thesecond reactant, the nitrogen may be flowed at a flow rate between about500 sccm and 10 slm.

Operation 111 may correspond to second reactant with plasma exposurephase 260A. As shown in FIG. 2, during 260A, the plasma and secondreactant are turned on, with an optional purge or carrier gas, while thefirst precursor flow is turned off. In many embodiments, the substrateis exposed to the second reactant for a time between about 1 second andabout 60 seconds, or about 2.5 seconds, or about 30 seconds.

Returning to FIG. 1, in operation 113, the chamber is optionally purgedwith a purge gas. The purge gas may be any purge gas described abovewith respect to operation 105. The purge gas may be flowed for aduration sufficient to remove excess byproducts from the chamber. Thisoperation may correspond to purge phase 280A of FIG. 2, whereby thepurge gas flows while the first precursor, plasma, and second reactantare turned off.

In operation 115 of FIG. 1, it is determined whether the film has beendeposited to an adequate thickness. If not, operations 103-113 arerepeated in cycles. At least about two deposition cycles or more may beincluded in disclosed embodiments to deposit a desired film thickness.For example, between about 2 and about 50 cycles may be performed, orbetween about 2 and about 30 cycles, or between about 2 and about 20cycles, or between about 2 and about 10 cycles.

FIG. 2 depicts two deposition cycles 210A and 210B. As shown, indeposition cycle 210B, operations in FIG. 1 are repeated such that thesubstrate is exposed to the first precursor during first precursorexposure phase 220B, the chamber is purged in purge phase 240B, thesubstrate is exposed to a second reactant with plasma in operation 260B,and the chamber is purged yet again in purge phase 280B.

Apparatus

FIG. 3 depicts a schematic illustration of an embodiment of an atomiclayer deposition (ALD) process station 300 having a process chamber body302 for maintaining a low-pressure environment. A plurality of ALDprocess stations 300 may be included in a common low pressure processtool environment. For example, FIG. 4 depicts an embodiment of amulti-station processing tool 400. In some embodiments, one or morehardware parameters of ALD process station 300, including thosediscussed in detail below, may be adjusted programmatically by one ormore computer controllers 350.

ALD process station 300 fluidly communicates with reactant deliverysystem 301 for delivering process gases to a distribution showerhead306. Reactant delivery system 301 includes a mixing vessel 304 forblending and/or conditioning process gases for delivery to showerhead306. One or more mixing vessel inlet valves 320 may control introductionof process gases to mixing vessel 304.

As an example, the embodiment of FIG. 3 includes a vaporization point303 for vaporizing liquid reactant to be supplied to the mixing vessel304. In some embodiments, vaporization point 303 may be a heatedvaporizer. The saturated reactant vapor produced from such vaporizersmay condense in downstream delivery piping. Exposure of incompatiblegases to the condensed reactant may create small particles. These smallparticles may clog piping, impede valve operation, contaminatesubstrates, etc. Some approaches to addressing these issues involvepurging and/or evacuating the delivery piping to remove residualreactant. However, purging the delivery piping may increase processstation cycle time, degrading process station throughput. Thus, in someembodiments, delivery piping downstream of vaporization point 303 may beheat traced. In some examples, mixing vessel 304 may also be heattraced. In one non-limiting example, piping downstream of vaporizationpoint 303 has an increasing temperature profile extending fromapproximately 100° C. to approximately 150° C. at mixing vessel 304.

In some embodiments, liquid precursor or liquid reactant may bevaporized at a liquid injector. For example, a liquid injector mayinject pulses of a liquid reactant into a carrier gas stream upstream ofthe mixing vessel. In one embodiment, a liquid injector may vaporize thereactant by flashing the liquid from a higher pressure to a lowerpressure. In another example, a liquid injector may atomize the liquidinto dispersed microdroplets that are subsequently vaporized in a heateddelivery pipe. Smaller droplets may vaporize faster than largerdroplets, reducing a delay between liquid injection and completevaporization. Faster vaporization may reduce a length of pipingdownstream from vaporization point 303. In one scenario, a liquidinjector may be mounted directly to mixing vessel 304. In anotherscenario, a liquid injector may be mounted directly to showerhead 306.

In some embodiments, a liquid flow controller (LFC) upstream ofvaporization point 303 may be provided for controlling a mass flow ofliquid for vaporization and delivery to process station 300. Forexample, the LFC may include a thermal mass flow meter (MFM) locateddownstream of the LFC. A plunger valve of the LFC may then be adjustedresponsive to feedback control signals provided by aproportional-integral-derivative (PID) controller in electricalcommunication with the MFM. However, it may take one second or more tostabilize liquid flow using feedback control. This may extend a time fordosing a liquid reactant. Thus, in some embodiments, the LFC may bedynamically switched between a feedback control mode and a directcontrol mode. In some embodiments, this may be performed by disabling asense tube of the LFC and the PID controller.

Showerhead 306 distributes process gases toward substrate 312. In theembodiment shown in FIG. 3, the substrate 312 is located beneathshowerhead 306 and is shown resting on a pedestal 308. Showerhead 306may have any suitable shape, and may have any suitable number andarrangement of ports for distributing process gases to substrate 312.Example process gases include soak gases, first precursor gases, carriergases or purge gases, and second reactant gases.

In some embodiments, a microvolume 307 is located beneath showerhead306. Practicing disclosed embodiments in a microvolume rather than inthe entire volume of a process station may reduce reactant exposure andpurge times, may reduce times for altering process conditions (e.g.,pressure, temperature, etc.) may limit an exposure of process stationrobotics to process gases, etc. Example microvolume sizes include, butare not limited to, volumes between 0.1 liter and 2 liters. This alsoimpacts productivity throughput. In some embodiments, the disclosedembodiments are not performed in a microvolume.

In some embodiments, pedestal 308 may be raised or lowered to exposesubstrate 312 to microvolume 307 and/or to vary a volume of microvolume307. For example, in a substrate transfer phase, pedestal 308 may beraised to position substrate 312 within microvolume 307. In someembodiments, microvolume 307 may completely enclose substrate 312 aswell as a portion of pedestal 308 to create a region of high flowimpedance.

Optionally, pedestal 308 may be lowered and/or raised during portionsthe process to modulate process pressure, reactant concentration, etc.,within microvolume 307. In one scenario where process chamber body 302remains at a base pressure during the process, lowering pedestal 308 mayallow microvolume 307 to be evacuated. Example ratios of microvolume toprocess chamber volume include, but are not limited to, volume ratiosbetween 1:500 and 1:10. It will be appreciated that, in someembodiments, pedestal height may be adjusted programmatically by asuitable computer controller 350.

In another scenario, adjusting a height of pedestal 308 may allow aplasma density to be varied during plasma activation and/or treatmentcycles included in the process. At the conclusion of the process phase,pedestal 308 may be lowered during another substrate transfer phase toallow removal of substrate 312 from pedestal 308.

While the example microvolume variations described herein refer to aheight-adjustable pedestal, it will be appreciated that, in someembodiments, a position of showerhead 306 may be adjusted relative topedestal 308 to vary a volume of microvolume 307. Further, it will beappreciated that a vertical position of pedestal 308 and/or showerhead306 may be varied by any suitable mechanism within the scope of thepresent disclosure. In some embodiments, pedestal 308 may include arotational axis for rotating an orientation of substrate 312. It will beappreciated that, in some embodiments, one or more of these exampleadjustments may be performed programmatically by one or more suitablecomputer controllers 350.

In some embodiments where plasma may be used as discussed above,showerhead 306 and pedestal 308 electrically communicate with a radiofrequency (RF) power supply 314 and matching network 316 for powering aplasma. In some embodiments, the plasma energy may be controlled bycontrolling one or more of a process station pressure, a gasconcentration, an RF source power, an RF source frequency, and a plasmapower pulse timing. For example, RF power supply 314 and matchingnetwork 316 may be operated at any suitable power to form a plasmahaving a desired composition of radical species. Examples of suitablepowers are included above. Likewise, RF power supply 314 may provide RFpower of any suitable frequency. In some embodiments, RF power supply314 may be configured to control high- and low-frequency RF powersources independently of one another. Example low-frequency RFfrequencies may include, but are not limited to, frequencies between 50kHz and 500 kHz. Example high-frequency RF frequencies may include, butare not limited to, frequencies between 1.8 MHz and 2.45 GHz, forexample 2 MHz, 13.56 MHz, or 27 MHz. It will be appreciated that anysuitable parameters may be modulated discretely or continuously toprovide plasma energy for the surface reactions. In one non-limitingexample, the plasma power may be intermittently pulsed to reduce ionbombardment with the substrate surface relative to continuously poweredplasmas.

In some embodiments, the plasma may be monitored in-situ by one or moreplasma monitors. In one scenario, plasma power may be monitored by oneor more voltage, current sensors (e.g., VI probes). In another scenario,plasma density and/or process gas concentration may be measured by oneor more optical emission spectroscopy sensors (OES). In someembodiments, one or more plasma parameters may be programmaticallyadjusted based on measurements from such in-situ plasma monitors. Forexample, an OES sensor may be used in a feedback loop for providingprogrammatic control of plasma power. It will be appreciated that, insome embodiments, other monitors may be used to monitor the plasma andother process characteristics. Such monitors may include, but are notlimited to, infrared (IR) monitors, acoustic monitors, and pressuretransducers.

In some embodiments, instructions for a controller 350 may be providedvia input/output control (IOC) sequencing instructions. In one example,the instructions for setting conditions for a process phase may beincluded in a corresponding recipe phase of a process recipe. In somecases, process recipe phases may be sequentially arranged, so that allinstructions for a process phase are executed concurrently with thatprocess phase. In some embodiments, instructions for setting one or morereactor parameters may be included in a recipe phase. For example, afirst recipe phase may include instructions for setting a flow rate ofan inert and/or a reactant gas (e.g., the second reactant) as a soakgas, instructions for setting a flow rate of a carrier gas (such asnitrogen), instructions for setting a pedestal temperature, and timedelay instructions for the first recipe phase. A second, subsequentrecipe phase may include instructions for modulating or stopping a flowrate of an inert and/or a reactant gas, and instructions for modulatinga flow rate of a carrier or purge gas and time delay instructions forthe second recipe phase. A third recipe phase may include instructionsfor setting a flow rate of an inert and/or reactant gas (e.g., the firstprecursor), instructions for modulating a flow rate of a carrier gas,and time delay instructions for the third recipe phase. A fourth recipephase may include instructions for modulating or stopping a flow rate ofan inert and/or a reactant gas, instructions for modulating the flowrate of a carrier or purge gas, and time delay instructions for thefourth recipe phase. A fifth recipe phase may include instructions forsetting a flow rate of an inert and/or reactant gas which may be thesame as or different from the gas used in the first recipe phase (e.g.,the second reactant), instructions for modulating a flow rate of acarrier gas, and time delay instructions for the fifth recipe phase. Itwill be appreciated that these recipe phases may be further subdividedand/or iterated in any suitable way within the scope of the presentdisclosure.

In some embodiments, pedestal 308 may be temperature controlled viaheater 310. The pedestal may be set to a deposition temperature. Forexample, the pedestal may be set to a temperature between about 200° C.and about 300° C. for deposition of a nitride or carbide. Further, insome embodiments, pressure control for process station 300 may beprovided by butterfly valve 318. As shown in the embodiment of FIG. 3,butterfly valve 318 throttles a vacuum provided by a downstream vacuumpump (not shown). However, in some embodiments, pressure control ofprocess station 300 may also be adjusted by varying a flow rate of oneor more gases introduced to the process station 300.

As described above, one or more process stations may be included in amulti-station processing tool. FIG. 4 shows a schematic view of anembodiment of a multi-station processing tool 400 with an inbound loadlock 402 and an outbound load lock 404, either or both of which maycomprise a remote plasma source. A robot 406, at atmospheric pressure,is configured to move substrates or wafers from a cassette loadedthrough a pod 408 into inbound load lock 402 via an atmospheric port410. A substrate is placed by the robot 406 on a pedestal 412 in theinbound load lock 402, the atmospheric port 410 is closed, and the loadlock is pumped down. Where the inbound load lock 402 comprises a remoteplasma source, the substrate may be exposed to a remote plasma treatmentin the load lock prior to being introduced into a processing chamber414. Further, the substrate also may be heated in the inbound load lock402 as well, for example, to remove moisture and adsorbed gases. Next, achamber transport port 416 to processing chamber 414 is opened, andanother robot (not shown) places the substrate into the reactor on apedestal of a first station shown in the reactor for processing. Whilethe embodiment depicted in FIG. 4 includes load locks, it will beappreciated that, in some embodiments, direct entry of a substrate intoa process station may be provided. In various embodiments, the soak gasis introduced to the station when the substrate is placed by the robot406 on the pedestal 412.

The depicted processing chamber 414 comprises four process stations,numbered from 1 to 4 in the embodiment shown in FIG. 4. Each station hasa heated pedestal (shown at 418 for station 1), and gas line inlets. Itwill be appreciated that in some embodiments, each process station mayhave different or multiple purposes. For example, in some embodiments, aprocess station may be switchable between an ALD and plasma-enhanced ALDprocess mode. Additionally or alternatively, in some embodiments,processing chamber 414 may include one or more matched pairs of ALD andplasma-enhanced ALD process stations. While the depicted processingchamber 414 includes four stations, it will be understood that aprocessing chamber according to the present disclosure may have anysuitable number of stations. For example, in some embodiments, aprocessing chamber may have five or more stations, while in otherembodiments a processing chamber may have three or fewer stations.

FIG. 4 depicts an embodiment of a wafer handling system for transferringsubstrates within processing chamber 414. In some embodiments, waferhandling system may transfer substrates between various process stationsand/or between a process station and a load lock. It will be appreciatedthat any suitable wafer handling system may be employed. Non-limitingexamples include wafer carousels and wafer handling robots. FIG. 4 alsodepicts an embodiment of a system controller 450 employed to controlprocess conditions and hardware states of process tool 400. Systemcontroller 450 may include one or more memory devices 456, one or moremass storage devices 454, and one or more processors 452. Processor 452may include a CPU or computer, analog and/or digital input/outputconnections, stepper motor controller boards, etc.

In some embodiments, system controller 450 controls all of theactivities of process tool 400. System controller 450 executes systemcontrol software 458 stored in mass storage device 454, loaded intomemory device 456, and executed on processor 452. Alternatively, thecontrol logic may be hard coded in the controller 450. ApplicationsSpecific Integrated Circuits, Programmable Logic Devices (e.g.,field-programmable gate arrays, or FPGAs) and the like may be used forthese purposes. In the following discussion, wherever “software” or“code” is used, functionally comparable hard coded logic may be used inits place. System control software 458 may include instructions forcontrolling the timing, mixture of gases, amount of gas flow, chamberand/or station pressure, chamber and/or station temperature, substratetemperature, target power levels, RF power levels, substrate pedestal,chuck and/or susceptor position, and other parameters of a particularprocess performed by process tool 400. System control software 458 maybe configured in any suitable way. For example, various process toolcomponent subroutines or control objects may be written to controloperation of the process tool components used to carry out variousprocess tool processes. System control software 458 may be coded in anysuitable computer readable programming language.

In some embodiments, system control software 458 may includeinput/output control (IOC) sequencing instructions for controlling thevarious parameters described above. Other computer software and/orprograms stored on mass storage device 454 and/or memory device 456associated with system controller 450 may be employed in someembodiments. Examples of programs or sections of programs for thispurpose include a substrate positioning program, a process gas controlprogram, a pressure control program, a heater control program, and aplasma control program.

A substrate positioning program may include program code for processtool components that are used to load the substrate onto pedestal 418and to control the spacing between the substrate and other parts ofprocess tool 400.

A process gas control program may include code for controlling gascomposition (e.g., first precursor gas, soak gas, second reactant gas,and purge gases as described herein) and flow rates and optionally forflowing gas into one or more process stations prior to deposition inorder to stabilize the pressure in the process station. A pressurecontrol program may include code for controlling the pressure in theprocess station by regulating, for example, a throttle valve in theexhaust system of the process station, a gas flow into the processstation, etc.

A heater control program may include code for controlling the current toa heating unit that is used to heat the substrate. Alternatively, theheater control program may control delivery of a heat transfer gas (suchas the soak gas) to the substrate.

A plasma control program may include code for setting RF power levelsapplied to the process electrodes in one or more process stations inaccordance with the embodiments herein.

A pressure control program may include code for maintaining the pressurein the reaction chamber in accordance with the embodiments herein.

In some embodiments, there may be a user interface associated withsystem controller 450. The user interface may include a display screen,graphical software displays of the apparatus and/or process conditions,and user input devices such as pointing devices, keyboards, touchscreens, microphones, etc.

In some embodiments, parameters adjusted by system controller 450 mayrelate to process conditions. Non-limiting examples include process gascomposition and flow rates, temperature, pressure, plasma conditions(such as RF bias power levels), pressure, temperature, etc. Theseparameters may be provided to the user in the form of a recipe, whichmay be entered utilizing the user interface.

Signals for monitoring the process may be provided by analog and/ordigital input connections of system controller 450 from various processtool sensors. The signals for controlling the process may be output onthe analog and digital output connections of process tool 400.Non-limiting examples of process tool sensors that may be monitoredinclude mass flow controllers, pressure sensors (such as manometers),thermocouples, etc. Appropriately programmed feedback and controlalgorithms may be used with data from these sensors to maintain processconditions.

System controller 450 may provide program instructions for implementingthe above-described deposition processes such as processes that employ asoak prior to initiating ALD for a substrate inserted into the reactionchamber, with the soak performed under any of the soak conditionsdescribed herein. The program instructions may control a variety ofprocess parameters, such as DC power level, RF bias power level,pressure, temperature, etc. The instructions may control the parametersto operate in-situ deposition of film stacks according to variousembodiments described herein.

The system controller will typically include one or more memory devicesand one or more processors configured to execute the instructions sothat the apparatus will perform a method in accordance with disclosedembodiments. Machine-readable media containing instructions forcontrolling process operations in accordance with disclosed embodimentsmay be coupled to the system controller.

In some implementations, the system controller 450 is part of a system,which may be part of the above-described examples. Such systems caninclude semiconductor processing equipment, including a processing toolor tools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The system controller 450, depending on theprocessing conditions and/or the type of system, may be programmed tocontrol any of the processes disclosed herein, including the delivery ofprocessing gases, temperature settings (e.g., heating and/or cooling),pressure settings, vacuum settings, power settings, radio frequency (RF)generator settings, RF matching circuit settings, frequency settings,flow rate settings, fluid delivery settings, positional and operationsettings, wafer transfers into and out of a tool and other transfertools and/or load locks connected to or interfaced with a specificsystem.

Broadly speaking, the system controller 450 may be defined aselectronics having various integrated circuits, logic, memory, and/orsoftware that receive instructions, issue instructions, controloperation, enable cleaning operations, enable endpoint measurements, andthe like. The integrated circuits may include chips in the form offirmware that store program instructions, digital signal processors(DSPs), chips defined as application specific integrated circuits(ASICs), and/or one or more microprocessors, or microcontrollers thatexecute program instructions (e.g., software). Program instructions maybe instructions communicated to the system controller 450 in the form ofvarious individual settings (or program files), defining operationalparameters for carrying out a particular process on or for asemiconductor wafer or to a system. The operational parameters may, insome embodiments, be part of a recipe defined by process engineers toaccomplish one or more processing steps during the fabrication of one ormore layers, materials, metals, oxides, silicon, silicon dioxide,surfaces, circuits, and/or dies of a wafer.

The system controller 450, in some implementations, may be a part of orcoupled to a computer that is integrated with, coupled to the system,otherwise networked to the system, or a combination thereof. Forexample, the system controller 450 may be in the “cloud” or all or apart of a fab host computer system, which can allow for remote access ofthe wafer processing. The computer may enable remote access to thesystem to monitor current progress of fabrication operations, examine ahistory of past fabrication operations, examine trends or performancemetrics from a plurality of fabrication operations, to change parametersof current processing, to set processing steps to follow a currentprocessing, or to start a new process. In some examples, a remotecomputer (e.g. a server) can provide process recipes to a system over anetwork, which may include a local network or the Internet. The remotecomputer may include a user interface that enables entry or programmingof parameters and/or settings, which are then communicated to the systemfrom the remote computer. In some examples, the system controller 450receives instructions in the form of data, which specify parameters foreach of the processing steps to be performed during one or moreoperations. It should be understood that the parameters may be specificto the type of process to be performed and the type of tool that thesystem controller 450 is configured to interface with or control. Thusas described above, the system controller 450 may be distributed, suchas by including one or more discrete controllers that are networkedtogether and working towards a common purpose, such as the processes andcontrols described herein. An example of a distributed controller forsuch purposes would be one or more integrated circuits on a chamber incommunication with one or more integrated circuits located remotely(such as at the platform level or as part of a remote computer) thatcombine to control a process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, an ALDchamber or module, an atomic layer etch (ALE) chamber or module, an ionimplantation chamber or module, a track chamber or module, and any othersemiconductor processing systems that may be associated or used in thefabrication and/or manufacturing of semiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the system controller 450 might communicate with one ormore of other tool circuits or modules, other tool components, clustertools, other tool interfaces, adjacent tools, neighboring tools, toolslocated throughout a factory, a main computer, another controller, ortools used in material transport that bring containers of wafers to andfrom tool locations and/or load ports in a semiconductor manufacturingfactory.

An appropriate apparatus for performing the methods disclosed herein isfurther discussed and described in U.S. patent application Ser. No.13/084,399, filed Apr. 11, 2011, and titled “PLASMA ACTIVATED CONFORMALFILM DEPOSITION”; and Ser. No. 13/084,305, filed Apr. 11, 2011, andtitled “SILICON NITRIDE FILMS AND METHODS,” each of which isincorporated herein in its entireties.

The apparatus/process described herein may be used in conjunction withlithographic patterning tools or processes, for example, for thefabrication or manufacture of semiconductor devices, displays, LEDs,photovoltaic panels and the like. Typically, though not necessarily,such tools/processes will be used or conducted together in a commonfabrication facility. Lithographic patterning of a film typicallyincludes some or all of the following operations, each operation enabledwith a number of possible tools: (1) application of photoresist on aworkpiece, i.e., substrate, using a spin-on or spray-on tool; (2) curingof photoresist using a hot plate or furnace or UV curing tool; (3)exposing the photoresist to visible or UV or x-ray light with a toolsuch as a wafer stepper; (4) developing the resist so as to selectivelyremove resist and thereby pattern it using a tool such as a wet bench;(5) transferring the resist pattern into an underlying film or workpieceby using a dry or plasma-assisted etching tool; and (6) removing theresist using a tool such as an RF or microwave plasma resist stripper.

EXPERIMENTAL Experiment 1

An experiment was conducted comparing film thickness between filmsdeposited by ALD using helium as a soak gas prior to ALD and filmsdeposited using gases to be used during the plasma environment operationof ALD prior to ALD. The pedestal was set to a temperature of 50° C.Substrates were placed on the pedestal to bring the substratetemperature up to 50° C. from room temperature.

In one trial, the substrate was exposed to a helium soak gas for sevenseconds prior to performing ALD cycles sufficient to deposit 8.8 Å ofsilicon oxide. Only 5.0 Å of silicon oxide was deposited. In a secondtrial, the substrate was exposed to an argon soak gas for nine secondsprior to performing ALD cycles sufficient to deposit 8.8 Å of siliconoxide. Argon was used as a carrier gas during the oxidant exposure withplasma in the ALD cycle. The thickness of the silicon oxide filmdeposited was 8.7 Å. In a third trial, the substrate was exposed to amixture of nitrous oxide (N₂O) and oxygen (O₂) for nine seconds prior toperforming ALD cycles sufficient to deposit 8.8 Å of silicon oxide. Thesame mixture of N₂O and O₂ was used in each cycle during the oxidantexposure with plasma phase. The thickness of the silicon oxide filmdeposited was 8.7 Å. In the fourth trial, the substrate was exposed tonitrogen (N₂) for nine seconds prior to performing ALD cycles sufficientto deposit 8.8 Å of silicon oxide. Nitrogen was used as a carrier gas ineach cycle during the oxidant exposure with plasma phase. The thicknessof the silicon oxide film deposited was 8.6 Å. As shown in Table 1below, films deposited using gases that were used in the second reactantphase with plasma of the ALD cycle achieved thicknesses closer to thethickness to be deposited as measured by the number of ALD cycles. Usinga helium soak resulted in a film thickness sufficiently lower thandesired.

TABLE 1 Thickness of Silicon Oxide Films Deposited with Soak Gases SoakChemistry Thickness Deposited Helium only 5.0 Å Ar 8.7 Å N₂O/O₂ 8.7 Å N₂8.6 Å

Experiment 2

An experiment was conducted to measure the wafer-to-wafer variationbetween films deposited using disclosed embodiments. One hundredsubstrates were deposited using the same sequence of ALD cycles in afour-station tool. The tool was indexed after sufficient cycles weredeposited for each substrate. Each time a substrate was inserted intothe tool, the tool introduced nitrogen (N₂) as a soak gas for 60 secondsbefore resuming the ALD cycles. Each ALD cycle included exposure to N₂,purging with N₂ purge gas, exposure to nitrous oxide (N₂O) and oxygen(O₂) and a plasma, and purging with N₂ purge gas. Each substrate wasexposed to sufficient ALD cycles to ideally deposit 8.8 Å of siliconoxide.

One set of experimental data obtained for thickness of films depositedfor various wafers is shown in FIG. 5. The line priming time for thisset of experimental data was 7 seconds. The wafers shown in FIG. 5yielded films with similar thickness at or around 8.8 Å, suggesting thatdisclosed embodiments can exhibit high consistency in repeatability.

CONCLUSION

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe appended claims. It should be noted that there are many alternativeways of implementing the processes, systems, and apparatus of thepresent embodiments. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein.

What is claimed is:
 1. A method for depositing silicon oxide films by plasma-enhanced atomic layer deposition on semiconductor substrates, the method comprising: (a) inserting a first semiconductor substrate into a chamber; (b) after inserting the first semiconductor substrate into the chamber and prior to performing a first cycle of plasma-enhanced atomic layer deposition (PEALD) at a deposition temperature, raising the first semiconductor substrate's temperature to about the deposition temperature by exposing the first semiconductor substrate to a helium-free soak gas for a duration of about 500 seconds or less to reduce wafer-to-wafer variation compared to semiconductor substrates processed using a helium-containing soak gas prior to performing the PEALD on a first semiconductor substrate; (c) performing the PEALD to deposit a first silicon oxide film on the first semiconductor substrate; and (d) after depositing the first silicon oxide film on the first semiconductor substrate, performing the PEALD in one or more cycles to deposit a second silicon oxide film on a second semiconductor substrate, wherein a cycle of the PEALD comprises exposing the substrate to a silicon-containing precursor in a non-plasma environment for a duration sufficient to substantially adsorb the silicon-containing precursor to a surface of the substrate and exposing the substrate to reactant gases comprising an inert gas and an oxidant in a plasma environment to form at least a portion of the silicon oxide film, wherein the soak gas contains the reactant gases, wherein the inert gas is selected from the group consisting of nitrogen, argon, and combinations thereof, wherein the oxidant selected from the group consisting of oxygen and nitrous oxide, and combinations thereof, and wherein the first silicon oxide film is deposited to a thickness of less than about 5 nm.
 2. The method of claim 1, wherein proportion of gases in the soak gas is substantially the same as proportion of the gases during the exposing of the substrate to the reactant gases in the cycle of PEALD.
 3. The method of claim 1, wherein flow rate of the soak gas in (b) is within about 10% of a maximum flow rate achievable by the chamber.
 4. The method of claim 3, wherein flow rate of the soak gas in (b) is at least about 15 slm.
 5. The method of claim 1, wherein flow rate of the soak gas in (b) is at least about 25% to about 200% of flow rate of the reactant gases.
 6. The method of claim 1, wherein wafer-to-wafer variation between average thickness of the first silicon oxide film and the second silicon oxide film is less than about ±2 Å.
 7. The method of claim 1, wherein between two and about fifty cycles of the PEALD are performed on each semiconductor substrate.
 8. The method of claim 1, wherein the first semiconductor substrate is exposed to the soak gas for a duration between about 5 seconds and about 60 seconds.
 9. The method of claim 1, wherein the soak gas is a temperature-stabilizing soak gas that stabilizes the first semiconductor substrate's temperature.
 10. The method of claim 1, wherein the wafer-to-wafer variation between average thickness of the first silicon oxide film and the second silicon oxide film is less than about ±2 Å.
 11. A method for depositing a film by plasma-enhanced atomic layer deposition on semiconductor substrates, the method comprising: (a) inserting a first semiconductor substrate into a chamber; and (b) after inserting the first semiconductor substrate into the chamber and prior to performing a first cycle of plasma-enhanced atomic layer deposition (PEALD) at a deposition temperature, raising the first semiconductor substrate's temperature to about the deposition temperature by exposing the first semiconductor substrate to a helium-free soak gas for a duration of about 500 seconds or less to reduce wafer-to-wafer variation compared to semiconductor substrates processed using a helium-containing soak gas prior to performing the PEALD on a first semiconductor substrate; (c) performing the PEALD to deposit a first film on the first semiconductor substrate; and (d) after depositing the first film on the first semiconductor substrate, performing the PEALD in one or more cycles to deposit a second film on a second semiconductor substrate, wherein a cycle of the PEALD comprises exposing the substrate to a precursor in a non-plasma environment for a duration sufficient to substantially adsorb the precursor to a surface of the substrate, exposing the substrate to a second reactant comprising an inert gas and oxygen-containing gas in a plasma environment to form at least a portion of the film, wherein the soak gas contains the second reactant wherein the inert gas is selected from the group consisting of nitrogen, argon, and combinations thereof, wherein the oxygen-containing gas is selected from the group consisting of oxygen and nitrous oxide, and combinations thereof, and wherein the first film is deposited to a thickness of less than about 5 nm.
 12. The method of claim 11, wherein the proportion of gases in the soak gas is substantially the same as the proportion of gases in the second reactant during the exposing of the substrate to the second reactant in the cycle of PEALD.
 13. The method of claim 11, wherein flow rate of the soak gas in (b) is within 10% of a maximum flow rate achievable by the chamber.
 14. The method of claim 13, wherein the flow rate of the soak gas in (b) is at least about 15 slm.
 15. The method of claim 11, wherein flow rate of the soak gas in (b) is at least about 25% to about 200% of the flow rate of the second reactant used when exposing the first semiconductor substrate to the second reactant in the plasma environment during the cycle of the PEALD.
 16. The method of claim 11, wherein the wafer-to-wafer variation of an average thickness of the first and second films deposited on at least the first and the second semiconductor substrates is less than about ±2 Å.
 17. The method of claim 11, wherein the soak gas is a temperature-stabilizing soak gas that stabilizes the first semiconductor substrate's temperature.
 18. A method for depositing silicon oxide films by plasma-enhanced atomic layer deposition on three or more semiconductor substrates, the method comprising: (a) inserting a first semiconductor substrate into a chamber; (b) after inserting the first semiconductor substrate into the chamber and prior to performing a first cycle of plasma-enhanced atomic layer deposition (PEALD) on the first semiconductor substrate at a deposition temperature, raising the first semiconductor substrate's temperature to about the deposition temperature by exposing the first semiconductor substrate to a helium-free soak gas for a duration of about 500 seconds or less; (c) performing n cycles of the PEALD to deposit a first silicon oxide film on the first semiconductor substrate; (d) after removing the first semiconductor substrate having the first silicon oxide film from the chamber and inserting a second semiconductor substrate into the chamber, performing the n cycles of the PEALD on the second semiconductor substrate to deposit a second silicon oxide film; and (f) after removing the second semiconductor substrate having the second silicon oxide film from the chamber and inserting a third semiconductor substrate into the chamber, performing the n cycles of the PEALD on the third semiconductor substrate to deposit a third silicon oxide film, wherein each of the n cycles of the PEALD comprises exposing the semiconductor substrate to a silicon-containing precursor in a non-plasma environment for a duration sufficient to substantially adsorb the silicon-containing precursor to a surface of the semiconductor substrate and exposing the semiconductor substrate to an oxidant in a plasma environment to form at least a portion of the silicon oxide film, wherein the helium-free soak gas contains one or more gases of the oxidant used when exposing the first semiconductor substrate to the oxidant in the plasma environment during the cycle of the PEALD, wherein the n cycles of PEALD are performed to deposit less than about 5 nm of silicon oxide on the second and third semiconductor substrates, and wherein wafer-to-wafer variation of an average thickness of the first, second, and third silicon oxide films deposited on the three or more semiconductor substrates is less than about ±2 Å.
 19. The method of claim 18, wherein the helium-free soak gas is a temperature-stabilizing soak gas that stabilizes the first semiconductor substrate's temperature. 